Displaying Disk Space Statistics (df)

Use the df command to show the amount of free disk space on
each mounted disk. The usable disk space that is reported by df
reflects only 90 percent of full capacity, as the reporting statistics allows for
10 percent above the total available space. This head room normally stays empty for better
performance.

The percentage of disk space actually reported by the df command is used
space divided by usable space.

If the file system exceeds 90 percent capacity, you could transfer files to
a disk that is not as full by using the cp command. Alternately,
you could transfer files to a tape by using the tar or
cpio commands. Or, you could remove the files.